1. Field of Invention
The present invention relates generally to plasma arc torch cutting machines and, in particular, relates to a positioning apparatus for positioning the torch.
2. Description of Related Art
Plasma arc torches are widely used for cutting metallic materials and can be employed in automated systems for automatically processing a work piece. The system may include the plasma arc torch, an associated power supply, a positioning apparatus, and an associated computerized numeric controller (CNC). At least one of the plasma arc torch and the work piece may be mounted on the positioning apparatus, which provides relative motion between the tip of the torch and the work piece to direct the plasma arc along a processing path.
The plasma arc torch generally includes a torch body, an electrode mounted within the body, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, a nozzle with a central exit orifice, electrical connections, and a power supply. The torch produces the plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum. A shield may also be employed on the tip of the torch to protect the nozzle and to provide a shield gas flow to the area proximate the plasma arc. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).
The power supply provides the electrical current necessary to generate the plasma arc. The power supply has one or more dc power modules to produce a constant current for the torch. Typically, the current can be set to discreet values. The power supply has a microprocessor, which regulates essentially all plasma system functions, including start sequence, CNC interface functions, gas and cut parameters, and shut off sequences. For example, the microprocessor can ramp-up or ramp-down the electrical current. The main on and off switch of the power supply can be controlled locally or remotely by the CNC. The power supply also powers a cooling system for cooling the torch.
The CNC communicates with the positioning apparatus to direct the motion of the torch to enable the work piece to be cut to a desired pattern. However, with some cut geometries, such as circles, prior art positioning systems that control the torch only in mutually orthogonal X, Y, and Z-axes produce a kerf that ends up being uneven as a small portion of the metal remains. Additionally, at times, it would be desired to cut the work piece with a bevel shaped edge. Therefore, there is a strong need to provide an improved positioning apparatus for a plasma torch system that enables the operator to better control the positioning of the torch to compensate for the angle of the side of the kerf or to provide a selected bevel cut.